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Climate Change Lengthening Pollen Season in U.S., Study Shows

Among the many disasters climate change is wreaking around the world, scientists have now identified a more personal one: It’s making allergy season worse.

That is the message of a new study in the journal Proceedings of the National Academy of Sciences published on Monday. The researchers found a strong link between planetary warming and pollen seasons that will make many of us dread spring just a little bit more.

According to the new paper, the combination of warming air and higher levels of carbon dioxide in the atmosphere has caused North American pollen seasons since 1990 to start some 20 days earlier, on average, and to have 21 percent more pollen.

Scientists have suggested for some time that the season is getting longer and more awful, and the new research provides greater detail and estimates of just how much a warming planet is responsible for the greater misery. They concluded that climate change caused about half of the trend in the pollen season, and 8 percent of the higher pollen count. What’s more, the trend of higher pollen counts, the researchers said, is accelerating.

The most pronounced effects were seen in Texas, the Midwest and the Southeast, said William Anderegg, an assistant professor of biology at the University of Utah and the lead author of the new study. The effects were less obvious in the northern United States, including New England and the Great Lakes states. The greatest pollen increases came from trees, as opposed to grasses and weeds, he said.

The researchers employed the techniques of attribution science, which is commonly used to state the degree to which extreme weather events like heat waves, wildfires or the amount of rain a hurricane brings are worse than they would have been in a world without climate change.

Applying this branch of science to pollen was a novel and welcome idea, said Kristie Ebi, a professor in the Center for Health and the Global Environment at the University of Washington who was not involved in the study. “It’s a great piece of work,” she said. “There has been very little research on the application of detection and attribution analysis to the health risks of a changing climate.”

The researchers looked at data gathered by 60 long-term pollen monitoring stations around the continental United States and compared the results with various climate models to find correlations. They also tried to discount potentially confounding factors, using satellite photos to determine whether changes in land use or tree growth during the period of the study near the pollen measuring stations could have skewed the results.

“The world’s a messy place,” Dr. Anderegg said, with many potentially confounding influences, “but the really strong signal here, and the attribution to climate change, is compelling.”

The paper concluded that “a clearly detectable and attributable fingerprint of human-caused climate on North American pollen loads provides a powerful example of how climate change is contributing to deleterious health impacts through worsening pollen seasons.”

Allergies are not just a case of the sniffles, of course: they have serious effects on public health, including asthma and other respiratory conditions. Studies have shown that students do less well in school during peak pollen season, and high-pollen periods have been associated with greater susceptibility to respiratory viruses — an ominous finding in the time of the coronavirus pandemic.

As for asthma, “It’s not a simple allergy, it’s a life-threatening condition,” said Amir Sapkota, a professor at the University of Maryland School of Public Health. His research suggests that early onset of pollen season correlates with a higher risk of hospitalization for asthma. What’s more, he noted, the impact of asthma is felt unevenly, with vulnerable populations living with a greater risk of severe disease because of lack of access to health care and the means to buy medication.

Dr. Ebi of the University of Washington cited figures from the Centers for Disease Control and Prevention that the United States has 24.8 million people with asthma, and 19 million adults reported having hay fever in the past 12 months. Seven million children had respiratory allergies over the same time period. The direct costs of pediatric asthma alone have been calculated at $5.9 billion in 2013, the latest figure cited in a 2019 study.

“This study shows climate change is now, and could affect the health of anybody with allergies or asthma” triggered by pollen, she said.

Dr. Anderegg suggested that more research into pollen’s effects should begin with more monitoring and measurement of pollen levels; there are far fewer pollen monitoring stations than those measuring particle pollutants and air quality. “We’re really under-monitoring pollen as an airborne pollutant,” he said.

The outlook, he said, is not a happy one. “We expect this to get worse in the next couple of decades.”

Dr. Anderegg added that the research has personal importance, as well. “I have to be on allergy medication eight months of the year,” he said, “and still there are periods when I’m still miserable during peak pollen season.”

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